1. Field of the Invention
The present invention relates to radio data transmitters and receivers in which power consumption is reduced.
2. Description of the Related Art
Nowadays, research on radio meter-reading systems for power, gas, and so forth is in progress. The radio meter-reading system enables a meter reader to measure consumption of power, gas, and so forth with a radio meter-reading apparatus from an automobile, without going to the place where the meters are installed.
A problem with the above type of conventional system is power consumption of a meter-reading apparatus while in standby mode. In other words, to activate the meter-reading apparatus by radio, the meter-reading apparatus must be standing by (That is in a condition capable of receiving radio waves). Accordingly, a receiving circuit must always be activated. However, maintaining the active state of the receiving circuit increases power consumption. For example, when a meter-reading apparatus is activated by a battery of small capacity, the power consumption of the receiving circuit severely shortens the life of the battery. In particular, since meter-reading apparatus is activated only once a month, it is not preferable that the receiving circuit consume wasted power for the remaining 29 days (or 30 days).